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Abstract

Purpose: To compare motor and cognitive performance in infants with typical development in the 1st, 2nd, 3rd, 6th, 9th, and 12th months after birth.

Methods: This was a repeated-measures study with unequal sample sizes in the follow-up periods, comprising 94 infants born at term. Infants with genetic syndromes, malformations, congenital infections, or hospitalized in intensive care units were excluded. The Bayley Scales of Infant Development II were used for evaluation of cognitive and motor performance.

Results: There were significant differences between motor and cognitive performance at 1, 2, and 3 months. However, at 6, 9, and 12 months, there was no difference between domains.

Conclusion: This study suggests that during the first year, development can be synchronous in the 2 areas evaluated by the Bayley Scales of Infant Development II, especially from the sixth month of age onward.

INTRODUCTION

Over the last 25 years, a significant increase in motor development research has appeared in top-tier journals of human development, psychology, and neuroscience.1–4 This attraction is due to the fact that the motor system is the easiest to observe and indicative of central nervous system maturity and integrity, as well as the child's global well-being, mainly during the first year of life. Complementing this finding, the literature indicates that there is a resurgence of interest in the relationship between early motor and cognitive abilities.5–8

Some authors believe that motor development and cognitive development may be fundamentally interrelated. Contrary to popular notions that motor development begins and ends early, whereas cognitive development begins and ends later, both motor development and cognitive development display equally protracted developmental timetables. When there are genetic or environmental concerns that affect the motor system or cognition, it is often the case that both motor and cognitive functions are affected.6

It has been suggested that motor development may act as a “control parameter” for further development, in that some motor abilities may be a prerequisite for the acquisition or practice of other developmental functions such as perceptual or cognitive ability. Bushnell and Boudreau9 provided support for this, with their study showing evidence that object perception occurred as a result of haptic exploration in infants. Biringen et al10 and Campos et al11 have furthered this argument, showing how the timing or age of reaching developmental milestones can produce different developmental outcomes. Adding to these, Wijnroks and Van Veldhoven12 found that infants with poorer postural control at 6 months had lower scores on the Mental scale of the Bayley Scales of Infant Development II (BSID II), were less successful in problem solving, and less attentive, 6 to18 months later, than infants with good postural control.

Past research has found a relationship between motor ability and working memory,13 motor ability and processing speed,14 and early motor development and later cognitive function15 in school-aged children. On the other hand, little evidence exists regarding the relationship between the developmental domains in children with typical development (TD) during the first year of life. Recent studies on infant cognition and motor development are scarce and the results are not conclusive.7 With this in mind, the question posed by this study was “Are motor and cognitive developmental domains comparable at early ages?” To answer this question, this study aimed to compare motor and cognitive performance of infants with TD at the 1st, 2nd, 3rd, 6th, 9th, and 12th months following birth.

It was hypothesized that motor and cognitive developmental domains are comparable, given the motor requirements (eg, stability, mobility) needed for exploring, learning, and socializing. Considering that there are few studies on the comparison of developmental domains in infants, especially during the first months of life, this study contributes to the increase of knowledge about the motor-cognition relationship, which may have implications for developmental assessment and therapeutic strategies.

METHODS

The research design consisted of a repeated-measures study with unequal sample sizes in the follow-up periods (1st, 2nd, 3rd, 6th, 9th, and 12th months) of infants born full-term with TD. This project was approved by the Research Ethics Committee at the Medical School of the University of Campinas (UNICAMP) (process no. 087/03), according to the provisions and principles of resolution 196/96 of the National Health Council.

A neonatologist selected 125 neonates delivered at the Neonatology Service of the Center of Integral Attention to Women's Health (CAISM), University of Campinas (UNICAMP). The subjects were selected using the following criteria: (1) subjects living in the metropolitan area of Campinas; (2) newborns of single-fetus pregnancies; (3) considered to be in good health, allowing them to go home within 2 days of birth; (4) gestational age categorized as full-term (37–41 weeks) by the Capurro method; and (5) parents willing to sign the consent forms. Neonates with genetic syndromes, multiple congenital malformations, and congenital infections (syphilis, toxoplasmosis, rubella, cytomegalovirus infection, and herpes) were excluded.

From the initial selected sample (N = 125), 94 infants returned for at least 1 assessment during the first year. The sample comprised all infants who came for follow-up assessments during each month: 61 infants at 1 month, 67 infants at 2 months, 67 infants at 3 months, 66 infants at 6 months, 60 infants at 9 months, and 68 infants at 12 months. Twenty infants were evaluated in all months (1st, 2nd, 3rd, 6th, 9th, and 12th), 32 infants were tested during 5 assessments, 12 infants were tested during 4 assessments, 14 infants were tested during 3 assessments, 8 infants were tested during 2 assessments, and 8 infants had only 1 test session.

Development was assessed using the BSID II,16 which include 100 items for testing cognition and 72 items for testing motor behavior during the first 12 months. The Cognitive scale includes items that assess memory, habituation, problem solving, early numeric concepts, generalization, classification, vocalizations, language, and social skills. The Motor scale includes items that test control of gross and fine muscle groups (movements associated with rolling, crawling and creeping, sitting, standing, walking, running, and jumping; motor manipulations involved in prehension, adaptive writing implements, and hand movement imitation). The cognitive and motor raw scores were obtained by adding the total number of items for which the child received credit on each scale and all items below the basal item (the first item in the item set for which the child receives credit). For both Cognitive and Motor scales, the raw scores were converted into standardized points designated the index score (IS), with a mean of 100 (SD = 15). On the basis of the IS, the infants were classified as presenting with accelerated performance (IS ≥ 115), within normal performance limits (IS = 85–114), mildly delayed performance (IS = 70–84), or significantly delayed performance (IS ≤69).16 In this study, the IS was used as an indicator of cognitive and motor performance and considered in the analysis of the data obtained.

The infants were assessed at the Laboratory for Study of Child Development at UNICAMP. The testing room was quiet, well lit, well ventilated, without bright or colorful pictures, and free of distractions. All infants were assessed in the presence of their mothers during intervals between feeds, when infants were alert and cooperative. The infants were evaluated at 1, 2, 3, 6, 9, and 12 months of age and the range permitted was 7 days before or after the respective age of examination.16

Examinations were performed by an examiner and simultaneously monitored by 2 observers. The testers included a developmental neurologist, a pediatrician, and a physical therapist—all members of the Interdisciplinary Group for Infant Development Evaluation. Prior to the examinations, the testers participated in reliability training for the BSID II, consisting of a didactic session of approximately 20 hours; each tester observed 12 videotaped tests and scored these independently. The intraclass correlation coefficient was 0.95 (P < .001), with a 95% confidence interval of 0.88 to 0.98.

Statistical analyses were performed using the Statistical Package for Social Sciences for Personal Computer (SPSS/PC 11.0). The α level adopted for rejection of the null hypothesis was less than .05. The data were presented using position and dispersion measurements for numerical variables and frequencies for categorical variables. The comparison between motor and cognitive performance in each month was investigated with the Wilcoxon signed rank test for abnormal distribution and the t test, when the values presented normal distribution.

RESULTS

The sample characteristics at birth are shown in Table 1. The sample was composed of infants born at-term who were not at risk for asphyxia: the 5-minute Apgar score was 8 or more in 100%. However, some infants were small for gestational age.

Regarding the family profile, 88.6% of parents were married, 84.8% of mothers had a low education level (≤8 years of study), and 66.3% of them did not work out of the home. For 49.4% of mothers, this was their first infant; 69.1% were between 21 and 35 years of age. The families were largely poor, and more than half of them (64.6%) had incomes below the poverty line (≤0.5 minimum wages per capita per month, equivalent to <$140).

The Figure shows the cognitive and motor IS in each month. With respect to the cognitive IS, the interval of development in infants was within the reference range (100 ± 15) during all evaluated periods. In contrast to cognitive performance, the infants presented with a mean motor IS below 85 at 3 months of age. It is important to note that infants scored below the BSID II mean for the period measured. Moreover, great variability in motor skills at 12 months of age was observed .

Table 2 presents the comparison between motor and cognitive domains at each age of assessment. There was a significant differences between motor and cognitive IS at 1, 2, and 3 months. However, at 6, 9, and 12 months, there was no difference between domains.

DISCUSSION

The focus of this study was the comparison between motor and cognitive developmental domains during the first year after birth. The results showed significant differences between motor and cognitive performance at 1, 2, and 3 months. However, at 6, 9, and 12 months, there was no difference between domains. What are the possible clinical implications of our results? Often a “statistically significant” result has no “clinical relevance” because the limit of the range of scores is still below the value considered important. This is often not taken into account and may lead to conclusions based on statistical results, without assessing the real significance of the difference detected.17

Some authors suggest that there is large variability in scores within a single infant, among infants, and across developmental domains. In that sense, a specific developmental domain may not demonstrate stability of scores over time, and different developmental domains may follow different developmental trajectories, so that an infant with TD could score high in one domain but low in another.7,18 According to Harris and Langkamp,19 the assumption that all areas of development progress simultaneously at an equal rate, or, conversely, would be equally delayed, is not supported in either typical or at-risk populations. It is believed that developmental change arises within a context as the product of multiple, developing elements. Some elements may be fully formed early in life but unseen because the supporting subsystems and processes are not ready. Other components may be comparatively delayed, and indeed one element may act as a “rate limiter,” preventing the cooperative self-organization of the other component. Only when all the components reach critical functioning and the context is appropriate does the system assemble a behavior.20 It is necessary, however, for further research to confirm these assumptions.

Neuromaturational theory explains the changes in developmental domains primarily by maturation of the central nervous system. On the basis of this premise, it is believed that different domains develop at a similar rate within a child. As such, the children tend to present similar abilities (as reflected in their test scores) across different developmental domains.21 The proposal that there is a relationship between motor development and cognitive development is not new. Previous scholars espouse this theory. According to Thelen22 Piaget proposed that activity and sensorimotor experience are important for the emergence of cognitive ability. For Piaget, cognition was built from perception and action, and Piaget's descriptions of how early motor skills such as reaching and sucking are used in the service of developing cognition, are still among the most insightful. Thelen pointed out that Gesell also believed that both domains (cognitive and motor development) were governed by the same developmental principles.22 Adding to this, Diamond6 argued for a close interrelationship between motor and cognitive development because brain structures, such as the striatum and neocerebellum, are involved in both motor and cognitive functions.

In a similar vein, Wijnroks and Van Veldhoven12 explored the relationship of individual differences in postural control and cognitive development. They were interested in whether postural dysfunctions would interfere with the exploration and manipulation of objects, as exploratory behavior is reported to be associated with cognitive development. In their study, 65 infants born preterm were observed during an exploration task at the corrected age of 6 months. It was found that infants with poorer postural control at 6 months had more difficulty with a problem-solving task than infants with good postural control. Murray et al23 also investigated motor and cognitive development. Their primary aim was to investigate the role of attaining developmental milestones and the relationship with executive functioning. It was found that infants who were able to stand earlier than their peers, scored higher on tests of adult categorization and categorization with working memory once they reached 33 to 35 years of age than did infants who were not able to stand until a later age.

Moreover, a study by Campos et al11 investigated the role of locomotor experience in social and emotional development, referential gestural communication, wariness of heights, the perception of self-motion, distance perception, spatial search, and spatial coding strategies. The results revealed that locomotion is a setting event, a control parameter, and a mobilizer that changes the intrapsychic states of the infant, the social and nonsocial world around the infant, and the interaction of the infant with that world. According to the authors, locomotion is not by itself a causal agent. The developmental changes found are not a function of locomotion per se; rather, the changes stem from the experiences that are engendered by independent mobility.

The results of the BSID II for infants in our study showed that their cognitive performance was within the normal interval (100 ± 15) during all evaluated periods. Conversely, their motor performance was below the BSID II mean at 3 months, at least lower than would be expected for infants with TD. This raises the question of what might account for this difference. It is possible that the infants who were small for gestational age contributed to reduce the sample motor score, because this condition represents a risk factor for motor development.3 Adding to this, the lack of validation of the developmental tests in developing countries may have contributed to the disadvantages observed in the infants studied. According to Bayley,16 the items within each set at each month ranged in difficulty from approximately 90% to 15% in infants completing the task. It is likely that there were particular items that were challenging for Brazilian infants.3

Explanations for lower scores of the infants in relation to the reference group may also be related to educational and cultural (child-rearing) variations between countries.3 Santos et al24 compared motor development among Brazilian infants with the reference group of the BSID II during the first year and verified significant differences between the groups during months 3, 4 and 5, where less than 15% of the Brazilian infants passed certain items related to grasping and sitting. It is believed that Brazilian mothers are more protective, infants are usually held on the mother's lap, and rarely placed on the floor to play during the first 6 months, limiting their gross motor development.24 Considering that the BSID II has not been culturally adapted to obtain reference values within the Brazilian population, caution should be exercised when making assumptions based on the data obtained.

This study has certain limitations that should to be taken into account when considering the possible contributions of the findings. First, the design does not permit analysis of changes over time; the variation in the number of infants assessed during each month could limit the observation of motor and cognitive development. Second, the sample size could have influenced the results, at least in part. A larger sample should be considered in future research. Future studies comparing developmental domains should be designed with these limitations in mind.

CONCLUSIONS

The results showed significant differences between motor and cognitive performance at 1, 2, and 3 months of age. However, at 6, 9, and 12 months, there was no difference between domains. This study suggests that development can be synchronous in the 2 areas evaluated for the BSID II, especially after 6 month of age. Motor and cognitive skills appear to be comparable and to develop dependently. So, it is necessary greater attention concerning these developmental domains during the first months of life to ensure optimal child development. Although this study provides relevant information about the comparison between motor and cognitive performance in infants with TD, further studies are needed to verify whether these findings can be applied to other samples.

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